Question

Module 14: Memory, OLED and Keypads Homework

Build an interactive calculator.

Use the OLED Display and matrix keypad to build a simple calculator application. The user presses the operands and operators using the keypad. The calculation output should be displayed on the OLED display. You may make the following simplifying assumptions.

a) Assume 1 digit numbers

b) Assume only two operators ‘+’ and ‘-’

Upload the breadboard diagram the code and a video.

Points 6: 2 points each for working and proper breadboard diagram, code and video.

Answer 1

Hi,

Here is the complete thing that we need, libraries that we need to include and complete code below:

Materials we need:

to make a calculator, we will need some kind of Processor, for which we can use Arduino, since this is a small project and needs large memory space for complicated code, we will use Arduino NANO.

for taking input number, we can use a 4x4 keypad with membrane switches, which has 4 rows and 4 columns, if we open up this sticker from behind, the flexible membrane PCB is visible, which has connections going from ROWS and COLUMNS to connecting pins via flexible PCB. When any membrane switch is pressed, the rows and column pins process the data as a Matrix and identify the location of key pressed.(Remember, left side pins are row pins and right side pins are column pins.)

for display we can use either OLED or LCD display, but I would like to use OLED, since the resolution of OLED is far better, we can have longer strings of numbers to operate, if we choose OLED.

Connections:

Now because we discudded above about the materials we needed, so now its the time to make connections now.

Below will be the steps for making connections:

1. connect Keypad to any digital pins on Arduino Nano ( preferably D2 to D9).
2. connect OLEDs SCL to Arduinos A5.

3. connect OLEDs SDA to Arduinos A4.

4. connect OLEDs VCC to Arduinos 5v.

5. connect OLEDs GND to Arduinos GND.

6. Connect a Switch between Positive of Lithium Polymer Battery.

7. Connect Lipo to 5V and Gnd pins of Arduino.

Code and libraries requires:

Below are the list of libraries required:

• SPI
• Keypad
• wire
• Adafruit SSD1306
• Adafruit GFX

Code:

#include <Keypad.h>
#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define OLED_RESET 4
Adafruit_SSD1306 display(OLED_RESET);

#if (SSD1306_LCDHEIGHT != 64)
#error("Height incorrect, please fix Adafruit_SSD1306.h!");
#endif

const byte numRows= 4; //number of rows on the keypad
const byte numCols= 4; //number of columns on the keypad

//keymap defines the key pressed according to the row and columns just as appears on the keypad
char customKey;
double first = 0;
long second = 0;
double total = 0;
char Operator;
bool equalPressed=false;
bool showFirst = false;

char keymap[numRows][numCols]=
{
{'1', '2', '3', '+'},
{'4', '5', '6', '-'},
{'7', '8', '9', 'x'},
{'C', '0', '=', '/'}
};

//Code that shows the the keypad connections to the arduino terminals
byte rowPins[numRows] = {9,8,7,6}; //Rows 0 to 3
byte colPins[numCols]= {5,4,3,2}; //Columns 0 to 3

//initializes an instance of the Keypad class
Keypad customKeypad= Keypad(makeKeymap(keymap), rowPins, colPins, numRows, numCols);

void showSplash() {
String splashString="Arduino Calculator by";
display.clearDisplay();
display.setTextSize(1);
display.setTextColor(WHITE);
display.setCursor(0,0);
display.setCursor(64-(splashString.length()*3),0);
display.print(splashString);
display.setTextSize(2);
splashString="Mission";
display.setCursor(64-(splashString.length()*6),16);
display.print(splashString);
display.setTextSize(2);
splashString="Critical";
display.setCursor(64-(splashString.length()*6),40);
display.print(splashString);
display.display();
delay(3000);
}

void setup()
{
Serial.begin(9600);
display.begin(SSD1306_SWITCHCAPVCC, 0x3C); // initialize with the I2C addr 0x3D (for the 128x64)
showSplash();
display.print("Arduino Calulator By Mission Critical");
display.setTextSize(2);
display.clearDisplay();
display.display();
}

void loop(){
customKey = customKeypad.getKey();
switch(customKey)
{
case '0' ... '9': // This keeps collecting the first value until a operator is pressed "+-*/"
showFirst=true;
first = first * 10 + (customKey - '0');
showDisplay();
break;

case '+':
showFirst=true;
Operator='+';
showDisplay();
second = SecondNumber(); // get the collected the second number
total = first + second;
showDisplay();
first = total, // reset values back to zero for next use
second = 0;   
break;

case '-':
showFirst=true;
Operator='-';
showDisplay();
second = SecondNumber();
total = first - second;
showDisplay();
first = total, second = 0;
break;

case 'x':
showFirst=true;
Operator='x';
showDisplay();
second = SecondNumber();
total = first * second;
showDisplay();
first = total, second = 0;
break;

case '/':
showFirst=true;
Operator='/';
showDisplay();
second = SecondNumber();
second == 0 ? display.print("Invalid") : total = (float)first / (float)second;
showDisplay();
first = total, second = 0;
break;

case 'C':
total = 0;
first=0;
second=0;
Operator='\0';
showFirst=false;
equalPressed=false;
display.clearDisplay();
display.display();
break;
}
}

void showDisplay()
{
display.clearDisplay();
display.setCursor(110,0);
display.println(Operator);
if (showFirst) {
Serial.print(first);
display.println(first);
} else
{
display.println("");
}
if (second>0) {
display.println(second);
} else
{
display.println("");
}
if (equalPressed) {
display.println(total);
equalPressed=false;
}
display.display();
}
long SecondNumber()
{
while( 1 )
{
customKey = customKeypad.getKey();
if(customKey >= '0' && customKey <= '9')
{
second = second * 10 + (customKey - '0');
showDisplay();
}

if(customKey == '=') {
equalPressed=true;
break; //return second;
}
}
return second;
}